Materials Science Lecture 8: Defects in Crystals

Flashcards covering the classification, definitions, and property impacts of various crystal defects including point, linear, planar, and volume imperfections.

What are some properties that are controlled or affected by defects in crystals?

Electric and thermal conductivity in metals, electronic conductivity in semiconductors, plastic deformation, colors, and mechanical strength.

How is a perfect crystal defined in materials science?

A crystal that contains no point, linear, or planar imperfections; it is an idealization that does not exist in nature.

What characterizes a real crystal compared to a perfect one?

Real crystals always have foreign atoms (impurities), missing atoms (vacancies), and atoms in between lattice sites (interstitials).

What are the four categories of crystal defects based on dimensionality?

0D (Point defects), 1D (Linear defects), 2D (Planar defects), and 3D (Bulk or volume defects).

Define 0D (Point defects).

Imperfect point-like regions in the crystal about the size of 1-2 atomic diameters, created by removal, addition, or displacement of an atomic species.

What are the common types of 0D Point Defects?

Vacancies, Impurities, Schottky defects, and Frenkel defects.

What is a vacancy defect?

A missing atom from an atomic site.

How does a vacancy move within a crystal?

If a neighboring atom moves to occupy the vacant site, the vacancy moves in the opposite direction to the site previously occupied by that atom.

What is the difference between an interstitial impurity and a substitutional impurity?

An interstitial impurity is a foreign atom sitting in the void of a crystal, whereas a substitutional impurity is a foreign atom replacing a parent atom.

What is a Schottky defect?

A defect created by removing one cation and one anion from the interior of an ionic crystal to maintain electrical neutrality and stoichiometry.

What is a Frenkel defect?

A defect formed when an atom or smaller ion (usually a cation) leaves its place in the lattice, creating a vacancy, and becomes an interstitial in a nearby location.

What are examples of 1D (Linear defects)?

Edge dislocations and screw dislocations.

What are examples of 2D (Planar defects)?

Grain boundaries, antiphase boundaries, stacking faults, twin boundaries, and external surfaces.

What are examples of 3D (Bulk or volume defects)?

Precipitates, dispersants, inclusions, and pores, voids, or cracks.

Which specific defect controls plastic deformation in crystalline materials?

Dislocation.

In which materials is electronic conductivity controlled by substitution defects?

Semiconductors.